This invention relates to the forming of bone cuts on a distal femur.
In particular, the application relates to forming an anterior bone cut, an anterior chamfer bone cut, a posterior bone cut and a posterior chamfer cut on a distal femur in which the distal bone cut has already been performed.
Total knee arthroplasty involves replacement of portions of the patella, femur and tibia with artificial components. In particular, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components. In performing this knee surgery, it has been desirable to minimize the size of the incision to thereby minimize damage to soft tissue.
In particular, it is necessary to resect the proximal tibia and distal femur with, among other cuts, a facing pair of planar cuts from which other bone cuts, in the case of the femur, can be referenced.
In order to make these cuts, resecting the femur and tibia necessitated significant cutting of soft tissue, including muscles, tendons and ligaments.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.
There are several types of knee prosthesis known in the art. One type is sometimes referred to as a “resurfacing type.” In these prostheses, the articular surface of the distal femur and the proximal tibia are “resurfaced” with respective metal and plastic condylar-type articular bearing components. Preferably, these components are made of titanium alloy or a cobalt-chrome alloy such as VITALLIUM® alloy.
One important aspect of these procedures is the correct resection of the distal femur and proximal tibia. These resections must provide planes which are correctly angled in order to properly accept and align the prosthetic components. In particular, the resection planes on the tibia and femur must be correctly located relative to at least three parameters: proximal-distal location; varus-valgus angle; and flexion-extension angle.
Moreover, following distal resection, the femur must be further shaped with the aid of a cutting block, the cutting block must be correctly located relative to internal-external rotation, medial-lateral position and anterior-posterior position. Recently, various computerized systems have been introduced to aid the practitioner during different surgical procedures. These systems improve accuracy of the cuts based on accurately locating the mechanical axis of the tibia and femur and provides the ability to verify the cuts made. In these systems, there is utilized multiple video cameras which are deployed above the surgical site and a plurality of dynamic reference frame devices also known as trackers. These trackers are attached to body parts and the surgical instruments and preferably include light emitting devices, such as light emitting diodes which are visible to the video cameras. Using software designed for a particular surgical procedure, a computer receiving input from the camera guides the placements of the surgical instruments with respect to landmarks on the body. Such systems are shown in U.S. Pat. Nos. 6,385,475 and 6,514,259, the teachings of which are incorporated herein by reference.
In co-pending application, Ser. No. 10/768,520 assigned to the assignee of the present invention, an instrument for resecting the distal facing surface of the femur from the medial or lateral side is provided. It is desirable to have a cutting block system which can be attached on the medial or lateral side of the femur for performing the other four bone cuts on the distal femur. It is particularly advantageous to have a multi-piece, preferably, a three piece cutting block, which pieces can be assembled in a manner so that it can be mounted on the medial or lateral side of the right or left knee and still be able to make the four bone cuts.
The instrumentation of the present invention includes components for resecting four of the bone cuts on the distal femur and includes an alignment system for properly positioning the cutting guide surfaces utilizing an optical tracking system optically coupled to a computer system. The design of the multi-piece instruments of the present invention allows the resection of the distal end to be performed anteriorly-laterally as contrasted with the typical resection systems of the prior art in which the resections are all performed from the anterior direction.
U.S. Patent Publication No. 2003/0171757 relates to an instrument that permits resection of the proximal end of the tibia and distal end of the femur to be performed either medially or laterally.